Contention based multiple access is increasingly being used in various types of wireless networks. For example, a carrier sense multiple access (CSMA) protocol may use contention based multiple access. The CSMA protocol may be utilized for a wireless network, where a data packet is addressed or intended for a recipient, and where any other unintended recipient of the data packet in the wireless network stops transmission of its own data packets to reduce chances of collision. A medium access control (MAC) layer protection is usually used in a CSMA protocol, in which a device may reserve a time period for transmission, during which no other device within the network may transmit any data packet.
The CSMA protocol may be used in various types of wireless networks, including a wireless local area network employing, for example, Institute of Electrical and Electronics Engineers (IEEE) 802.11 protocols, e.g., IEEE 802.11b protocol released on 1999, IEEE 802.11g protocol released on 2003, IEEE 802.11n protocol expected to be released on 2009-2010, or any other appropriate IEEE 802.11 protocol. The CSMA protocol may also be used in other types of wireless networks, e.g., a wireless personal area network (WPAN), or the like.
FIG. 1 schematically illustrates an exemplary wireless network 100 including a plurality of wireless devices (e.g., device 1, . . . , device 5). The wireless network 100 may employ a CSMA protocol (e.g., any appropriate IEEE 802.11 protocol) to wirelessly communicate between the wireless devices 1, . . . , 5. Individual devices in the wireless network 100 transmit and/or receive data packets from one or more other devices in the network. For example, the wireless network 100 may be a wireless local area network (WLAN) employing an appropriate IEEE 802.11 protocol, and the device 1 may be an access point of the WLAN network. Devices 2, . . . , 5 may comprise computing devices (e.g., personal computers, laptops, etc.) that communicates with the access point of the network. Although only 5 wireless devices are illustrated in FIG. 1, any number of wireless devices may be included in the wireless network 100.
FIG. 2a illustrates an exemplary frame 200 transmitted by a wireless device (e.g., any of the wireless devices illustrated in FIG. 1). The frame 200 includes a preamble field 204, a signal field 210 (identified as Sig 210 in FIG. 2a), and a payload field 216. The preamble field 204 is used to indicate a start of the frame, and includes information that may be used by a recipient of the frame to perform a frequency and/or timing synchronization, automatic gain control (AGC), channel estimation, and/or the like.
The signal field 210 acts as a physical header for the frame, and includes one or more physical layer parameters of the frame. For example, the signal field 210 may include a modulation and/or coding scheme of the frame, a length of the payload, channel estimation information, and/or the like. The payload field 216 includes data, which may be modulated using one or more parameters indicated in the signal field 210. The payload field 216 may comprise a data packet.
Several other types of frame formats (e.g., non-high throughput (HT) format, HT mixed format, HT Greenfield format) may also used in a CSMA protocol (e.g., IEEE 802.11n protocol), as is known to those skilled in the art. For example, FIG. 2b illustrates an exemplary frame 200b, utilizing a non-high throughput format. The frame 200b may be used in a wireless network that utilizes, for example, IEEE 802.11n protocol. Similar to the frame 200, the frame 200b includes a payload field 216 and a signal field 210. The frame 200b also includes a preamble field comprising of a legacy short training field (L-STF) 220a and a legacy long training field (L-LTF) 220b. 
Referring again to FIG. 1, device 1 transmits a frame (e.g., frame 200 or 200a) addressed to, for example, device 3. Device 3 (i.e., the intended recipient), along with one or more of the other devices (e.g., devices 2, 4 and/or 5) in the network 100, receives the frame. That is, although a frame may be addressed to an intended device, one or more other devices in the network may also receive the frame.
Upon receiving a frame, a device (e.g., device 3) may not immediately know if the device is an intended recipient of the frame (e.g., if a destination address in the frame is the same or different from the device address). A destination address of the current frame may be included in a MAC header in the payload field 216.
Device 3, upon receiving the frame, extracts synchronization information, automatic gain control settings, and/or channel estimation information from the preamble field 204 of the frame. Device 3 also updates one or more physical parameter settings (e.g., synchronization parameters, automatic gain control parameters, channel estimation parameters, etc.) based on the extracted information from the preamble field 204 of the current frame. Device 3 decodes the signal field 210 to extract one or more physical layer parameters (e.g., length) of the frame. Once device 3 identifies a length of the frame (and the corresponding time needed to transmit the entire frame), device 3 generally does not transmit any of its own frames (e.g., to avoid chances of collision with the current frame).
Upon decoding the physical layer parameters, device 3 transmits these parameters, including a MAC header, to the MAC layer. The MAC layer of device 3 detect the destination address (e.g., included in the MAC header) of the frame. If device 3 determines that device 3 is the intended recipient of the frame (e.g., the destination address of the frame matches the address of device 3), device 3 further processes the payload data in the frame. Otherwise (e.g., if device 3 detects that it is not the intended recipient), device 3 disregards the frame and/or stops further processing of the data in the frame.
Two consecutive frames that are from the same source (e.g., the same transmitter) generally have one or more similar physical layer parameter (e.g., similar channel estimations). However, even if two consecutive frames (e.g., a first and second frame) are from the same source, a device may not know that the second frame has the same source address as the first frame until the device has already decoded one or more physical layer parameters from the second frame, and passed the decoded parameters to the MAC layer. Accordingly, each time a device receives a frame, the device generally needs to decode the one or more physical layer parameters from the frame, update its physical layer parameter settings, decode and transmit the MAC header (by decoding the payload field) to the MAC layer, and subsequently, the MAC layer determines the source and destination addresses of the frame. And if the frame is not addressed to the device, the device discards the physical layer parameter settings and stops further processing of the frame.
FIG. 3 schematically illustrates an exemplary receiver system 300 included in one of the devices (e.g., device 3) in the wireless network 100 of FIG. 1. The receiver system 300 includes two antennas 304a and 304b configured to transmit and/or receive wireless packets and frames to and/or from other wireless devices in the wireless network 100. Antennas 304a and 304b are operatively coupled to respective carrier sense and synchronization modules 308a and 308b. The respective carrier sense and synchronization modules 308a and 308b are also operatively coupled to channel estimation modules 312a and 312b, respectively. The channel estimation modules 312a and 312b are operatively coupled to a signal and payload demodulation/decoding module 320. The carrier sense and synchronization modules 308a and 308b are also coupled to a joint carrier sense (CS), synchronization, and AGC module 316. Also illustrated in FIG. 3 is a frame 324, which may be similar to the frame 200b of FIG. 2b, and which includes a preamble field (including legacy short training field (L-STF) 220a and legacy long training field (L-LTF) 220b), signal field 210 and a payload field 216.
In operation, the two antennas 304a and 304b receive a frame (e.g., frame 324), and the carrier sense and synchronization modules 308a and 308b extract frame and time synchronization information and a start of the frame indication from the preamble fields (e.g., L-STF field 220a and L-LTF field 220b) of the frame 324. The joint CS, synchronization, and AGC module 316 uses the extracted information from the carrier sense and synchronization modules 308a and 308b to provide a joint carrier sense, carrier synchronization and/or automatic gain control for the receiver system 300. The joint CS, synchronization, and AGC module 316, thus, combines information received from both the antennas 304 and 304b to achieve a relatively better performance. The channel estimation modules 312a and 312b perform channel estimation of the frame 324 (using, for example, information in L-LTF field 220b), and output the frame to signal and payload demodulation/decoding module 320 for further processing (e.g., demodulating and/or decoding the signal field 210 and/or the payload field 216).
The joint CS, synchronization, and AGC module 316 uses extracted information from carrier sense and synchronization modules 308a and 308b, thereby at least partially gaining from the antenna diversity or redundancy. However, the joint CS, synchronization, and AGC module 316 may not be able to fully exploit the advantages offered by multiple antenna diversity. This is because the joint CS, synchronization, and AGC module 316 may not have channel estimations of the receive frame.
In summary, as discussed with respect to FIG. 2a, until a device decodes the payload field 216 of a received frame and transmits the MAC header included in the payload field to the MAC layer of the device, the device may not know if the device is an intended recipient of the frame. Moreover, each time a device receives a frame, the device needs to extract one or more physical layer parameters from the frame and update the device's physical layer parameter settings. However, if the device is not the intended recipient of the frame, the device discards most of the decoded data and stops further processing of the frame. This generally results in waste of device resources, for example, device power. Also, as discussed with respect to FIG. 3, in a multi-antenna system, as the module 316 does not have access to channel estimation of a received frame, the module 316 may not be able to fully exploit advantages of multiple antenna diversity.